David Cameron urged his backbenchers and the rightwing media today to calm down over the government's plans to raise capital gains tax to 40%.

Cameron's remarks were made before his first big speech as prime minister, in which he called for a rebalanced economy with a greater role for manufacturing and a relatively smaller one for financial services.

Cameron made his speech alongside the business secretary, Vince Cable, who praised him for forming the coalition. The plan to raise capital gains tax is Cable's brainchild in his period as Liberal Democrat Treasury spokesman.

Cable sees the tax rise as necessary to finance his plans to raise personal allowances and stop anyone earning less than £10,000 from paying income tax. The coalition agreement calls for capital gains tax to be raised on non-business assets from its present 18% to 40%, with the change due to be introduced in the emergency budget next month. "What we're proposing here is a modest increase in capital gains tax revenue in order to pay for raising income tax allowances," Cameron said. So this is to help less well-off people, and I think that makes sense."

The Daily Telegraph, reflecting the mood on the Tory right, launched a campaign today to block the rise.

Cameron also highlighted the need to reopen world trade talks, also a theme of Gordon Brown that largely went unheeded. The prime minister hopes his plan to build stronger links with India may help undo some of the blockages to a trade deal, and will raise the issue at the G20 summit next month. Cameron's speech was also designed to counter the gloom of austerity Britain by saying the deficit reduction programme was designed to make the coming decade the most dynamic in Britain's history.

He also promised that he will oversee a new one in one rule, so that no business regulation can be introduced without another regulation being dismantled.

Cameron accused Labour of "endless interference" which had led Britain to being ranked 84th in the world for tax and 86th for regulation. Cameron promised the government would "get out of the way of business".

He also hinted that he would retain some of the industrial activism of the previous business secretary, Lord Mandelson, saying the government would not be a "bystander" but would promote enterprise, including beyond the south-east.

Cameron said under Labour, Britain had been "sleepwalking our way to an economy that is unsustainable, unstable, unfair and frankly uninspiring". The country had become 'over-reliant on welfare … hostile to enterprise ... far too dependent on the public sector [and] indebted on an unprecedented scale".

The former Labour cabinet minister David Blunkett said the true rise in worklessness and number of people on the welfare rolls came under Lady Thatcher's government in the 1980s when tens of thousands were parked on to incapacity benefit.

Blunkett said: "That scandal was tackled by the Labour government from 1997. To now pretend that we are not one of the best nations in the world – better than anywhere else in Europe – in terms of the percentage of the population who are economically active is a deceit towards the British people."

"There is no point in re-fighting the general election of May 6, but there is every point in avoiding history being rewritten, lies being told and the achievements of the Labour government being binned.

"The people must not be misled into believing – even if they like the rhetoric – that the Conservative party are the best force for alleviating poverty and overcoming unemployment.

The shadow industry secretary Pat McFadden asked: "How can the prime minister talk about the importance of manufacturing when he is planning to cut investment allowances to support manufacturing in order to give a corporation tax cut to parts of the economy that don't rely on investment — a policy described by the Engineering Employers' Federation as a disaster?

"How can he talk about refocusing RDAs when one of his government's first acts has been to cut their budgets by almost £300 million this year."